The present invention relates generally to a binocular stereoscopic viewing device and in particular to a binocular indirect ophthalmoscope for stereoscopic observation of the fundus of the eye.
In binocular ophthalmoscopic examinations, the examiner's pupils and an observation light source must be reflected to the pupil of the eye to be examined. For good stereoscopic vision, images of the examiner's pupils must be separated from each other as far as possible. In order to receive as few interfering reflexes as possible from the cornea of the patient's eye, the image of the light source should be separated as far as possible from the images of the examiner's pupils. These conditions can be met satisfactorily if the pupil of the patient is dilated by the application of a drug. There are, however, cases in which a dilation of the pupil is impossible or impractical, and to stereoscopically view a patient's pupil in such cases, binocular indirect ophthalmoscopes were developed in which relative separation of the images of the examiner's pupils and of the light source can be adjusted to the size of the patient's pupil.
U.S. Pat. No. 4,449,797 (Kocher et al.) discloses a binocular indirect ophthalmoscope comprising an observation unit and an illumination unit connected thereto. The observation unit contains two mirrors arranged in a wedge for reflecting images of the examiner's pupils to the patient's pupil along optical observation axes forming an observation plane extending from the observation unit toward a patient. The two mirrors are displaceable in the observation plane making it possible to alter the angle of convergence of the optical observation axes between the mirrors and the patient's pupil, and hence, the position of the images of the examiner's pupils relative to the patient's pupil. The illumination unit contains another mirror which can be raised, lowered or tilted, to change the optical axis of light projected from the light source and thus the position of the light source relative to the patient's pupil.
A similar ophthalmoscope is described in the article by K.R. Hovland et al. titled "Clinical Evaluation of the Small-Pupil Binocular Indirect Ophthalmoscope", published in "Archives of Ophthalmology", October 1969, Volume 82, pages 466-474. In the ophthalmoscope described in this article, the two observation mirrors are also arranged in a wedge displaceable in the observation plane, and the third mirror for reflecting illumination from the light source is independently displaceable parallel to the observation plane, making it possible to independently adjust the angle of convergence of the images of the examiner's pupils and the position of the image of the light source relative to the patient's pupil.
In both of the above-described ophalmoscopes, the examiner has to actuate two operating controls in order to adjust the optical axes of observation and the optical axis of illumination and position images of the examiner's pupils and the light source within the respective size of the patients's pupil. It is particularly difficult for a less skilled examiner to coordinate the separate operating controls for moving the observation mirrors and the illumination mirror by alternating actuation of the controls in such a way to optimize stereoscopic viewing of the fundus of the patient's eye without interference from disturbing reflections. Adjusting such ophthalmoscopes for narrow pupils of patients is difficult even for an experienced examiner, so that an exact adjustment is frequently dispensed with for reasons of time, and the examiner is satisfied with monocular observation of the fundus of the eye.
U.S. Pat. No. 3,963,329 (Stumph et al.) discloses a binocular indirect ophthalmoscope also of the type having two observation mirrors arranged in a wedge for reflecting the examiner's pupils from respective eyepieces, and an illumination mirror for reflecting light. The illumination axis is adjusted by moving the illumination mirror with one control, and the observation axes are adjusted by moving the eyepieces. Thus, two separate adjustments have to be made to adjust the observation axes and the illumination axis.
U.S. Pat. No. 4,196,966 (Malis) discloses a binocular magnification unit which includes a pyramid-shaped reflector having three reflective surfaces.